Method and apparatus for delivering precursors

ABSTRACT

A method and apparatus for delivering precursors to a chemical vapor deposition or atomic layer deposition chamber is provided. The apparatus includes a temperature-controlled vessel containing a precursor. An energy source is used to vaporize the precursor at its surface such that substantially no thermal decomposition of the remaining precursor occurs. The energy source may include a carrier gas, a radio frequency coupling device, or an infrared irradiation source. After the precursor is exposed to the energy source, the vaporized portion of the precursor is transported via a temperature-controlled conduit to a chemical vapor deposition or atomic deposition chamber for further processing.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a division of U.S. patent application Ser.No. 10/223,175, filed Aug. 19, 2002.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to a method and apparatus fordelivering precursors for use in chemical vapor deposition (CVD) oratomic layer deposition (ALD) processes, and more particularly, to theuse of an energy source to vaporize and deliver the precursors to aprocess or reaction chamber without subjecting the precursors to bulkthermal decomposition.

[0003] Chemical vapor deposition (CVD) has been extensively used forpreparation of films and coatings in semiconductor wafer processing. CVDis a favored deposition process in many respects because of its abilityto provide highly conformal and high quality films at relatively fastprocessing times. Further, CVD is beneficial in coating substrates ofirregular shapes, including the provision of highly conformal films evenwith respect to deep contacts and other openings.

[0004] Atomic layer deposition (ALD) is a relatively new process whichis becoming favored as a method for achieving uniform thin depositionlayers. While ALD is a slower process than CVD, ALD allows the use ofprecursors which are higher in reactivity because the chemical speciesare injected independently into an ALD reactor, which in turn allowsprocessing at lower temperatures than conventional CVD processes.

[0005] Standard CVD and ALD processes employ precursor sources invaporization chambers that are separated from the process or reactorchamber where the deposition surface or wafer is located. Liquidprecursors are typically placed in bubblers and heated to a temperatureat which they vaporize, and the vaporized liquid precursor material isthen transported by a carrier gas passing over the bubbler or throughthe liquid precursor. The vapors are swept through a gas line to theprocess or reaction chamber for depositing a CVD or ALD film on a heatedsubstrate or wafer. Many techniques have been developed to preciselycontrol this process, and the amount of material transported to theprocess chamber can be precisely controlled by, for example, thetemperature of the liquid precursor reservoir and by the flow of thecarrier gas bubbled through or passed over the reservoir.

[0006] For example, Mikoshiba et al, U.S. Pat. No. 5,476,547 describes agas feeding device which bubbles a carrier gas through a liquidorganometallic precursor. Huston et al, U.S. Pat. No. 6,179,277 andVaartstra et al, U.S. Pat. No. 6,244,575, both describe two-stepvaporization systems for liquid organometallic precursors.

[0007] However, similar techniques have not been adequate for vaporizingsolid precursors suitable for depositing CVD and ALD films. Forillustration, similar techniques may include bulk sublimation of thesolid precursor with transport of the vaporized solid precursor to theprocess chamber using a carrier gas in a manner similar to the transportof the vaporized liquid precursor. Solid precursors have generally beenconsidered to be poor choices for CVD and ALD processes due to thedifficulty of vaporizing, i.e. subliming, a solid at a controlled rateto provide a reproducible flow of vapor. However, there are manyoff-the-shelf solid precursors available, particularly solidorganometallic precursors, which, if they could be delivered effectivelyand reproducibly, could be used in CVD and ALD processes.

[0008] Lack of control of solid precursor sublimation is due, at leastin part, to the changing surface area of the bulk solid precursor as itis vaporized. Such a changing surface area when the bulk solid precursoris exposed to sublimation temperatures produces a continuously changingrate of vaporization, particularly for thermally sensitive compounds.This ever changing rate of vaporization results in a continuouslychanging and nonreproducible flow of vaporized solid precursor deliveredfor deposition to the process chamber. As a result, film growth rate andcomposition of such films deposited on wafers in the process chamberusing such vaporized solid precursors cannot be controlled adequatelyand effectively.

[0009] Therefore, it is important to precisely control the exposure ofthe solid precursors to elevated temperatures to avoid bulkdecomposition of the solid precursor material. However, many solidprecursors, such as organometallic precursors, decompose slowly whenheld near their sublimation temperatures. This prevents the use of acontinuously heated chemical ampoule or other vessel to maintain anelevated vapor pressure.

[0010] Accordingly, there remains a need in the art for a vapor deliverysystem for delivering both solid and liquid precursors, particularlythermally sensitive precursors for use in a CVD or ALD process, at aprecisely controllable rate and without bulk decomposition of theprecursor material during vaporization.

SUMMARY OF THE INVENTION

[0011] The present invention meets that need by providing a method andapparatus for delivering gaseous precursors to a CVD or ALD process thatovercomes the above-mentioned problems by controlling the rate ofvaporization at the surface of the precursor while avoiding bulk thermaldecomposition of the precursor. Thus, the precursor is a phase changematerial which undergoes a change in phase from solid or liquid to agaseous vapor during processing.

[0012] According to one aspect of the present invention, a method isprovided for vaporizing a material such as a precursor in which aprecursor vaporizer, preferably in the form of an energy source, is usedto vaporize a portion of a precursor. The precursor is vaporized byexposing the surface of the precursor to the energy source. By “energysource”, it is meant a source which is capable of increasing temperatureto provide evaporation or sublimation of a material such as a precursor.Preferably, the energy source is selected from the group consisting of agas, a radio frequency coupling device, and an infrared irradiationsource.

[0013] Where the energy source comprises a gas, the gas preferably has atemperature of at least about 20° C. higher than the precursor.Generally, the temperature of the gas will be between about 10° C. toabout 300° C., and more preferably, between about 50° C. to about 300°C. The gas is preferably a carrier gas which is non-reactive with theprecursor. Suitable carrier gases include those selected from the groupconsisting of nitrogen, helium, and argon, or a combination thereof.

[0014] The precursor is preferably present in solid or liquid form andundergoes a phase change to a gaseous vapor when exposed to the energysource. The energy source vaporizes the surface of the precursor withoutheating the entire volume of the precursor such that substantially nothermal decomposition of the remaining precursor occurs. By“substantially no thermal decomposition” it is meant that the majorityof the mass of the precursor maintains its thermal stability. In apreferred embodiment, the vaporized portion of the precursor is thentransported to a deposition chamber such as a chemical vapor depositionor atomic layer deposition chamber for further processing.

[0015] Precursors suitable for use in the method of the presentinvention include both organic and inorganic metal-containing compounds.The precursors may be either in a solid or liquid form, depending uponthe temperature at which the precursors are maintained and undergo aphase change during processing. As used herein, the term “metal organic”includes metal organic compounds having a central atom bonded to atleast one carbon atom of a ligand as well as compounds having a centralatom bonded directly to atoms other than carbon in a ligand. Preferredprecursors include metal organic precursors which have at least onemetal selected from the group consisting of Sr, Ba, Sc, Y, La, Ce, Ti,Zr, Hf, Pr, V, Nb, Ta, Nd, Cr, W, Pm Mn, Re, Sm, Fe, Ru, Eu, Co, Rh, Ir,Gd, Ni, Tb, Cu, Dy, Ho, Al, Tl, Er, Sn, Pb, Tm, Bi, Yb, and Si.

[0016] For example, where it is desired to deposit a titanium-containingmaterial, the precursor will contain titanium (Ti). Suitable precursorcompounds containing titanium include tetrakis-dimethyl aminotitanium,tetrakis-diethyl aminotitanium, bis(2,4-dimethyl-1,3-pentadienyl)titanium cyclopentadienyl cycloheptatrienyl titanium,dicyclooctatetraene titanium, and biscyclopentadienyltitanium diazide.Known titanium-containing liquid precursors include titaniumtetrachloride, and tetrakisdimethylamidotitanium (TDMAT). Knownsilicon-containing precursors include tetraethoxysilane, tetraethylorthosilicate (TEOS). Where it is desired to deposit different metals,other known precursor compounds may be utilized.

[0017] In embodiments where the method is used to vaporize a solidprecursor, the method includes exposing the surface of the solidprecursor to an energy source such that the solid precursor issublimated at its surface, preferably without heating the entire volumeof the precursor.

[0018] An apparatus used in accordance with the present invention fordelivering gaseous precursors includes a temperature-controlled vesselcontaining a solid or liquid precursor and an energy source. The energysource is preferably selected from the group consisting of a heated gas,a radio frequency coupling device, and an infrared radiation source.Preferably, the precursor is contained in a temperature-controlledvessel such as an ampoule. The vessel also includes an outlet configuredto pass vaporized precursor therethrough. The apparatus further includesa temperature-controlled conduit communicating with the outletconfigured to deliver the vaporized precursor to a deposition chambersuch as a chemical vapor deposition or atomic layer deposition chamber.

[0019] Where the energy source comprises a gas, the vessel preferablyincludes an inlet for receiving the gas. The temperature of the gasentering the vessel is preferably at least about 20° C. higher than thetemperature of the bulk precursor compound contained in the vessel.While the gas need not be heated if that condition is met, typically theapparatus also preferably includes a heater connected to the inlet forheating the gas prior to entering the vessel. The gas is preferablyheated to a temperature of between about 10° C. to about 300° C. priorto entering the vessel.

[0020] Where the energy source comprises a radio frequency couplingdevice or an infrared irradiation source, these sources are preferablylocated outside the vessel and act on a surface of the precursor in thevessel.

[0021] Accordingly, it is a feature of the present invention to providea method and apparatus for vaporizing and delivering precursors to achemical vapor deposition or atomic layer deposition chamber withsubstantially no bulk thermal decomposition of the precursor. These, andother features and advantages of the present invention, will becomeapparent from the following detailed description, the accompanyingdrawings, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 is a schematic view of an apparatus for vaporizing anddelivering a precursor in accordance with one embodiment of the presentinvention;

[0023]FIG. 2 is a schematic view of the apparatus including a radiofrequency (rf) coupling device in accordance with an alternativeembodiment of the present invention; and

[0024]FIG. 3 is a schematic view of the apparatus including an infrared(IR) irradiation device in accordance with another alternativeembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] The method and apparatus of the present invention provide severaladvantages over prior methods of vaporizing and delivering precursors.In the present invention, the energy source is used to control the rateof sublimation of a solid precursor or control the rate of evaporationof a liquid precursor at the surface of the precursor so that the masstransport of the vaporized precursor to the process or reaction chamberis accelerated. By controlling the rate of vaporization at the surfaceof the precursor, the entire volume of the precursor is not heated andsubstantially no thermal decomposition of the remaining precursoroccurs.

[0026] Further, the thermal mass of the ampoule vessel along with themass of the precursor acts to reduce or negate the temperature increasein the bulk of the precursor caused by heated carrier gas passingthrough the vessel. Thus, the vessel acts as a stabilizing mass as wellas a heat sink to prevent the temperature of the bulk precursor fromrising to a level where thermal decomposition occurs.

[0027] The method and apparatus of the present invention allows thevaporized precursor to remain in a thermally stable condition forfurther processing in a chemical vapor deposition or atomic layerdeposition chamber. Decomposition of the precursor that might occur dueto long term exposure to elevated temperatures is reduced or eliminated.This, in turn, eliminates or reduces costs involved in replacingprecursors that have degraded due to thermal exposure.

[0028] Suitable precursors for use in the present invention include bothsolid and liquid precursors that have heretofore been used in thesemiconductor processing industry to produce metal-containing depositedmaterials. Preferred precursors include metal organic precursors whichhave at least one metal selected from the group consisting of Sr, Ba,Sc, Y, La, Ce, Ti, Zr, Hf, Pr, V, Nb, Ta, Nd, Cr, W, Pm Mn, Re, Sm, Fe,Ru, Eu, Co, Rh, Ir, Gd, Ni, Tb, Cu, Dy, Ho, Al, Tl, Er, Sn, Pb, Tm, Bi,Yb, and Si.

[0029] For example, where it is desired to deposit a titanium-containingmaterial, the precursor will contain titanium (Ti). Suitable precursorcompounds containing titanium include of tetrakis-dimethylaminotitanium, tetrakis-diethyl aminotitanium,bis(2,4-dimethyl-1,3-pentadienyl) titanium cyclopentadienylcycloheptatrienyl titanium, dicyclooctatetraene titanium, andbiscyclopentadienyltitanium diazide. Known titanium-containing liquidprecursors include titanium tetrachloride, andtetrakisdimethylamidotitanium (TDMAT). Known silicon-containingprecursors include tetraethoxysilane, tetraethyl orthosilicate (TEOS).Where it is desired to deposit different metals, other known precursorcompounds may be utilized.

[0030] Referring now to FIG. 1, an apparatus 10 for vaporizing anddelivering precursors to a chemical vapor deposition or atomic layerdeposition chamber is shown. The apparatus 10 includes a vessel 12 suchas an ampoule that contains a solid or liquid precursor 14. The vessel12 is preferably comprised of a thermally conductive material that isnon-reactive with the precursor. Suitable thermally conductive materialsinclude metals such as stainless steel and/or aluminum. The vessel 12 isof a suitable size and capacity for the amount of precursor required foruse in the process. For vaporization of solid or liquid precursors, thetemperature of the vessel is preferably controlled at a temperature offrom between about −200° C. to about 200° C. Heating and/or coolingelements may be used to control the temperature within a desired range.

[0031] In the embodiment shown, a carrier gas 16 is used as the energysource for vaporizing the precursor which undergoes a phase change fromits bulk solid or liquid form. By “carrier gas”, it is meant a gas orcombination of gases that are non-reactive with the precursor under theprocessing conditions used. The carrier gas may comprise any of a numberof inert gases including helium, nitrogen, neon, argon, or a combinationthereof. In the embodiment that is shown, the apparatus includes a gasheater 18 for preheating the carrier gas prior to entering the vessel12. Suitably, the temperature of the carrier gas need be only about 20°C. higher than the temperature of the precursor, although, dependingupon the volume of precursor needed, the flow rate of the carrier gas,and the vapor pressure of the precursor, a greater temperaturedifferential may be useful. The carrier gas is preferably heated to atemperature of between about 10° C. and about 300° C., and morepreferably, between about 50° C. and about 300° C. It should beappreciated that the temperature of the gas will vary depending on thetemperature and vapor pressure of the precursor, the composition of theprecursor, and other process parameters such as flow rates, etc. Thecarrier gas is preferably heated to a temperature so as to be theprimary source of heat for vaporizing the solid or liquid precursor.

[0032] The vessel includes an inlet 20 for receiving the carrier gas 16.The desired carrier gas flows through a conduit 22 and is controlled byvalves 24 and 26. The carrier gas enters the vessel 12 through inlet 20and is flowed over the surface area of the precursor 14 such that theprecursor is vaporized at its surface.

[0033] The vaporized portion of the precursor 14 then exits the vessel12 through an outlet 28 controlled by outlet valve 30 and is carriedalong with the carrier gas through a conduit 32 to a chemical vapordeposition or atomic layer deposition chamber 34. The vaporizedprecursor can then be processed as desired in the chamber 34.

[0034] The conduit 22 and the conduit 32 may comprise stainless steeltubing or the like. The tubing is sized to provide the necessary volumeof materials to the deposition chamber. The conduit 32 is preferablymaintained at temperature that is conducive to the thermal stability ofthe particular precursor being used. The temperature of the conduit maybe maintained at a temperature that is less than, equal to, or greaterthan the temperature of the heated carrier gas.

[0035]FIG. 2 illustrates an alternative embodiment of the invention inwhich the apparatus includes an rf coupling device 40 which is used asthe energy source for vaporizing the precursor. As shown, device 40 islocated outside the vessel but may also be located inside the vessel.The device utilizes radio frequency current to vaporize the precursor 14at its surface by flash vaporization. The vaporized precursor is thencarried by carrier gas 16 and exits the vessel 12 through outlet 28 forfurther processing as described above. It should be appreciated that inthis embodiment, the carrier gas is not heated and does not act as anenergy source, but it used to carry the vaporized precursor to thechamber 34. However, it is within the scope of the present invention toutilize both the rf coupling device 40 and carrier gas as dual energysources.

[0036]FIG. 3 illustrates another alternative embodiment of the inventionin which the apparatus includes an IR radiation source 42 as the energysource. The radiation source may be located inside or outside thevessel. The solid or liquid precursor 14 is vaporized at its surface bythe radiation via flash vaporization. The vaporized precursor is thentransported by the carrier gas 16 to the processing chamber as describedabove. Again, the carrier gas may either be unheated and simply used asa transport mechanism, or may be used in combination with the radiationsource as dual sources of energy.

[0037] While certain representative embodiments and details have beenshown for the purpose of illustrating the invention, it will be apparentto those skilled in the art that various changes in the methods andapparatus disclosed herein may be made without departing from the scopeof the invention, which is defined in the appended claims.

What is claimed is:
 1. An apparatus for delivering precursors to adeposition chamber comprising: a temperature-controlled vesselconfigured to contain a solid or liquid precursor; said vessel includingan outlet configured to pass a gaseous precursor therethrough; an energysource; and a temperature-controlled conduit connected to said outletconfigured to deliver the gaseous precursor to a deposition chamber. 2.The apparatus of claim 1 wherein said energy source is selected from thegroup consisting of a gas, a radio frequency coupling device, and aninfrared irradiation source.
 3. The apparatus of claim 2 wherein saidenergy source comprises a gas and said vessel includes an inletconfigured to receive said gas.
 4. The apparatus of claim 3 furtherincluding a heater configured to heat said gas prior to entering saidvessel.
 5. The apparatus of claim 1 wherein said energy source comprisesa gas having a temperature of at least about 20° C. higher than saidsolid or liquid precursor.
 6. The apparatus of claim 5 wherein thetemperature of said gas is between about 10° to about 300° C.
 7. Theapparatus of claim 5 wherein the temperature of said gas is betweenabout 50° C. to about 300° C.
 8. The apparatus of claim 3 wherein saidgas is a carrier gas selected from the group consisting of nitrogen,helium, neon, and argon, or a combination thereof.
 9. The apparatus ofclaim 1 in which said energy source comprises a radio frequency couplingdevice and said apparatus further includes a source of a carrier gas.10. The apparatus of claim 9 wherein said carrier gas is heated and isused as an energy source in combination with said radio frequencycoupling device.
 11. The apparatus of claim 9 wherein said radiofrequency coupling device is located inside said vessel.
 12. Theapparatus of claim 9 wherein said radio frequency coupling device islocated outside said vessel.
 13. The apparatus of claim 1 in which saidenergy source comprises an infrared radiation source and said apparatusfurther includes a source of a carrier gas.
 14. The apparatus of claim13 wherein said carrier gas is heated and is used as an energy source incombination with said infrared radiation source.
 15. The apparatus ofclaim 13 wherein said infrared radiation source is located inside saidvessel.
 16. The apparatus of claim 13 wherein said infrared radiationsource is located outside said vessel.
 17. The apparatus of claim 1wherein said solid or liquid precursor comprises a metal organiccompound.
 18. The apparatus of claim 17 wherein said metal organiccompound contains at least one metal selected from the group consistingof Sr, Ba, Sc, Y, La, Ce, Ti, Zr, Hf, Pr, V, Nb, Ta, Nd, Cr, W, Pm Mn,Re, Sm, Fe, Ru, Eu, Co, Rh, Ir, Gd, Ni, Tb, Cu, Dy, Ho, Al, Ti, Er, Sn,Pb, Tm, Bi, Yb, and Si.
 19. The apparatus of claim 18 wherein said metalcomprises Ti.
 20. The apparatus of claim 17 where said metal organiccompound is selected from the group consisting of tetrakis-dimethylaminotitanium, tetrakis-diethyl aminotitanium,bis(2,4-dimethyl-1,3-pentadienyl) titanium cyclopentadienylcycloheptatrienyl titanium, dicyclooctatetraene titanium, andbiscyclopentadienyltitanium diazide.
 21. The apparatus of claim 1wherein said precursor comprises a liquid and is selected from the groupconsisting of tetraethoxysilane, tetraethyl orthosilicate, titaniumtetrachloride, and tetrakisdimethylamidotitanium.
 22. The apparatus ofclaim 1 wherein said vessel is comprised of a thermally conductivematerial.
 23. In combination, a temperature-controlled vessel configuredto contain a solid or liquid precursor therein; said vessel including anoutlet configured to pass a vaporized portion of said precursortherethrough; and a deposition chamber for receiving and processing thevaporized portion of said precursor.